Japanese Laid-Open Patent Publication No. 2004-258620 (hereinafter “Document 1”) discloses the realization of a projection optical system which, in addition to using an image forming optical system including a reflective surface to increase the size on the screen of projected images while reducing the projection space outside a projector apparatus, is capable of correcting chromatic aberration and also an image projecting apparatus that uses such projection optical system. To do so, Document 1 discloses that a first and second optical system are disposed in that order from a light valve on the projection side of the light valve, the first optical system includes at least one refractive optical system and has positive refractive power, the second optical system includes at least one reflective surface with refractive power and has positive refractive power, an image formed by the light valve is formed into an intermediate image on the optical path of the first and second optical systems, and the intermediate image is enlarged further and projected onto a screen.
Japanese Laid-Open Patent Publication No. 2004-295107 (hereinafter “Document 2”) discloses a technology that realizes a variable magnification optical system that is compact and achieves a desired zoom ratio while suppressing the occurrence of various aberrations such as lateral chromatic aberration. The variable magnification optical system in Document 2 is composed of an optical block R including three reflective curved surfaces and an optical block C disposed on the reducing side of the optical block R, the optical block C includes a plurality of movable lens units, and zooming is carried out by moving the plurality of lens units. When tracing the optical axis from the reducing side to the enlargement side, the optical block C forms an image at a reducing side conjugate point that is closer to the enlargement side than the optical surface (reflective surface) closest to the reducing side in the optical block R.
In a variety of applications such as presentations and education in schools, there is demand for a projection lens system that is more compact and capable of being made more wide angle.